Method for collecting metal

ABSTRACT

It is an object of the present invention to collect a scarce metal such as iridium from a light-emitting element which is no longer used. A method for collecting a metal is provided in which an organic metal compound which can emit visible light from a triplet excited state at room temperature is heated, or an EL layer of a light-emitting layer containing an organic metal compound which can emit visible light from a triplet excited state at room temperature is dissolved in a solvent to form a solution, and the solution is heated, irradiated with microwaves or treated with acid water. According to the above method, resources of metals such as iridium or platinum, which are scarce metals, can be utilized efficiently.

TECHNICAL FIELD

The present invention relates to a method for collecting a metalcontained in an electroluminescent light-emitting element.

BACKGROUND ART

In recent years, research and development have been carried out activelyfor electroluminescent light-emitting elements. A basic structure ofthese light-emitting elements is that a light-emitting substance issandwiched between a pair of electrodes. The application of voltage tothis element enables the light-emitting substance to emit light.

Since such light-emitting elements are of a self-luminous type, theyhave advantages such as having higher visibility compared with liquidcrystal displays and no need of back lights. Therefore, theselight-emitting elements are suitable for flat panel display elements.Another significant advantage is that such light-emitting elements canbe manufactured to be thin and light-weight. Another feature is thatthese light-emitting elements have extremely high response speed.

Since these light-emitting elements can be formed in a film form, planarlight emission can easily be obtained by forming elements with largeareas. Planar light emission is hard to obtain from point-light sourcessuch as incandescent lamps and LEDs, or line sources such as fluorescentlights. Therefore, these light-emitting elements have a high utilityvalue as surface illuminants. The surface illuminants can be applied tolighting and the like.

Electroluminescent light-emitting elements are largely classified intotwo types according to whether the light-emitting substance is anorganic compound or an inorganic compound. Here the light-emittingsubstance which is the organic compound is described.

When the light-emitting substance is an organic compound, theapplication of voltage to the light-emitting element makes electronsinjected from an electrode into a layer containing the light-emittingorganic compound, holes injected from the other electrode into the layercontaining the light-emitting organic compound, and then electriccurrent flows. Then, the recombination of these carriers (electrons andholes) excites the light-emitting organic compound. The light-emittingorganic compound emits light in returning to a ground state. Because ofsuch mechanism, such a light-emitting element is referred to as alight-emitting element of a current excitation type.

Excitation states of an organic compound can be classified into twotypes: a singlet excited state (S*) and a triplet excited state (T*).The statistical generation ratio of the singlet excited state (S*) andthe triplet excited state (T*) in a light-emitting element is consideredto be S*:T*=1:3.

A ground state of a light-emitting organic compound is usually a singletstate. Therefore, light emission in returning to a singlet ground statefrom a singlet excited state (S*) is referred to as fluorescence sinceit is caused by electronic transition between the same multiplets. Onthe other hand, light emission in returning to a singlet ground statefrom a triplet excited state (T*) is referred to as phosphorescencesince it is caused by electronic transition between differentmultiplets. In most of the compounds which emit fluorescence(hereinafter referred to as “fluorescent compounds”), only fluorescenceis observed and phosphorescence is not at room temperature. Therefore,the maximum value of the internal quantum efficiency (the ratio ofphotons to be generated with respect to injected carriers) of alight-emitting element containing a fluorescent compound is said to betheoretically 25%, on grounds that S*:T*=1:3.

On the other hand, by using a compound which emits phosphorescence(hereinafter referred to as a “phosphorescent compound”), an internalquantum efficiency of 75 to 100% is possible in theory. In other words,it is possible to achieve light emission efficiency which is three tofour times that of a fluorescent compound. For such a reason, alight-emitting element using a phosphorescent compound is proposed inorder to achieve a highly efficient light-emitting element (for example,refer to Non-Patent Document 1: Tetsuo TSUTSUI et al., “Japanese Journalof Applied Physics” vol. 38, 1999, pp. L1502-L1504)

As a phosphorescent compound, a complex containing iridium (Ir) as acentral metal is used in general as in Non-Patent Document 1. However,iridium is a noble metal and exists in crusts in extremely smallamounts. Accordingly, there arises a problem of resource depletion ofiridium, as light-emitting devices and electronic appliances usinglight-emitting elements come into wide use. In addition, in order toreduce adverse impact on the environment, methods for reusing iridiumare needed.

DISCLOSURE OF INVENTION

The present invention has been devised in view of the above problems. Anobject of the present invention is to provide a method for collecting ascarce metal such as iridium from a light-emitting element no longerneeded.

An aspect of the present invention is a method for collecting metal froman organic metal compound, including a step of ashing an EL layer of alight-emitting element containing an organic metal compound which canemit visible light in returning to a singlet ground state from a tripletexcited state at room temperature through heat treatment. In thisspecification, the EL layer denotes a layer provided between a pair ofelectrodes in a light-emitting element.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a step of performing aheat treatment at a temperature of 800° C. or higher on an EL layer of alight-emitting element containing an organic metal compound which canemit visible light in returning to a singlet ground state from a tripletexcited state at room temperature.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a step of performing aheat treatment at a temperature of 800° C. or higher under atmosphericair or an oxygen atmosphere on an EL layer of a light-emitting elementcontaining an organic metal compound which can emit visible light inreturning to a singlet ground state from a triplet excited state at roomtemperature, and collecting a metal oxide which remains after the heattreatment.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a step of performing aheat treatment on an EL layer of a light-emitting element containing anorganic metal compound at a temperature of 800° C. or higher under areducing atmosphere or with a reducing agent, and collecting a metaloxide which remains after the heat treatment.

In the above structure, the remaining metal or the remaining metal oxidemay be treated with acid water after the heat treatment, and a solutionin which a metal compound containing the metal which constitutes theorganic metal compound is dissolved may be obtained. As the acid water,water containing any of the following can be used: hydrogen chloride,hydrogen bromide, hydrogen fluoride, hydrogen iodide, sulfuric acid,nitric acid, nitrous acid, and acetic acid.

In the above structure, a step of oxidizing the solution in which themetal compound is dissolved may be included.

In the above structure, a step of electrolyzing the solution in whichthe metal compound is dissolved may be included.

In the above structure, a step of reacting the metal contained in thesolution in which the metal compound is dissolved and an organic ligandto form a metal complex may be included.

In the above structure, a step of reacting the metal contained in thesolution in which the metal compound is dissolved and an organic ligandto form a metal complex, and a step of extracting the metal complex witha solvent which dissolves the metal complex may be included. In thiscase, it is preferable that the solvent be not uniformly mixed withwater.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a first step of exposingan EL layer by detaching one in a pair of electrodes included in alight-emitting element from the light-emitting element in which the ELlayer containing an organic metal compound which can emit visible lightin returning to a singlet ground state from a triplet excited state atroom temperature is formed between the pair of electrodes, and a secondstep of irradiating a solution in which the EL layer is dissolved in asolvent with microwaves.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a first step of exposingan EL layer by detaching one in a pair of electrodes included in alight-emitting element from the light-emitting element in which the ELlayer containing an organic metal compound which can emit visible lightin returning to a singlet ground state from a triplet excited state atroom temperature is formed between the pair of electrodes, and a secondstep of adding an organic compound to a solution in which the EL layeris dissolved in a solvent and performing microwave irradiation.

In the above structure, a third step may be included in which a solutionin which the metal compound containing the metal which constitutes theorganic metal compound is dissolved or a suspension in which the metalcompound is suspended is formed by treating the solution irradiated withthe microwaves with a solvent containing acid water.

Another aspect of the present invention is a method for collecting ametal from an organic metal compound, including a first step of exposingan EL layer by detaching one in a pair of electrodes included in alight-emitting element from the light-emitting element in which the ELlayer containing an organic metal compound which can emit visible lightin returning to a singlet ground state from a triplet excited state atroom temperature is formed between the pair of electrodes, and a secondstep of forming a solution in which the metal compound containing themetal which constitutes the organic metal compound is dissolved or asuspension in which the metal compound is suspended, by treating the ELlayer of the light-emitting element with a solvent containing acidwater.

In the above structure, as the acid water, water containing any of thefollowing can be used: hydrogen chloride, hydrogen bromide, hydrogenfluoride, hydrogen iodide, sulfuric acid, nitric acid, nitrous acid, andacetic acid.

In the above method, a step of oxidizing the solution in which the metalcompound is dissolved or the suspension in which the metal complex issuspended may be included.

In the above structure, a step of electrolyzing the solution in whichthe metal compound is dissolved may be included.

In the above structure, a step of forming a metal complex by reactingthe metal contained in the solution in which the metal compound isdissolved or the suspension in which the metal complex is suspended andan organic ligand may be included.

In the above structure, a step of forming a metal complex by reactingthe metal contained in the solution in which the metal compound isdissolved or the suspension in which the metal complex is suspended andan organic ligand, and a step of extracting the metal complex using asolvent which dissolves the metal complex may be included.

In the above structure, the organic ligand is supported by a highmolecular compound, and the metal complex may be formed by mixing theorganic ligand supported by the high molecular compound and the solutionor a mixture containing the metal compound.

In the above structure, it is preferable that the organic ligand be anyof the following: an amine derivative, an ethylenediamine derivative, atriethylenediamine derivative, an ethylenediaminethiocarboaldehydederivative, a phenol derivative, a polyphenol derivative, a thiolderivative, a cyclic thiol derivative, an ether derivative, a cyclicether derivative, a uracil derivative, an amide derivative, ammoniumsalt, a pyridine derivative, an amino sulfide derivative, an anilinederivative, a phosphoric acid derivative, phosphonium salt, a phosphineoxide derivative, a thiourea derivative, a benzothiazole derivative, ora thiocarbonyl derivative.

In the above structure, it is preferable that the metal belong to any ofthe groups 7 to 11 in the periodic table. Further, it is preferable thatthe metal be Ir, Pt, Ru, or Re. Furthermore, it is preferable that themetal be a rare earth metal.

According to the present invention, resources of metals such as iridium(Ir) and platinum (Pt), which are scarce metals, can be utilizedefficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a light-emitting element.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment modes of the present invention are described in detailhereinafter with reference to the diagram. Note that the presentinvention is not limited to the following description and it is easilyunderstood by those skilled in the art that the modes and detailsdisclosed herein can be modified in various ways without departing fromthe spirit and the scope of the present invention. Therefore, thepresent invention should not be interpreted as being limited to thedescription of the embodiment modes to be given below.

Embodiment Mode 1

This embodiment mode describes a method for collecting a metal atom froma light-emitting element containing an organic metal compound which canemit visible light in returning to a singlet ground state from a tripletexcited state at room temperature.

FIG. 1 shows a structure of a general light-emitting element. Thelight-emitting element shown in FIG. 1 is formed over a substrate 201and includes a first electrode 202, an EL layer 203, and a secondelectrode 204. The EL layer 203 is sandwiched between the firstelectrode 202 and the second electrode 204, and contains an organicmetal compound which can emit visible light in returning to a singletground state from a triplet excited state at room temperature. To bemore specific, the EL layer 203 contains a metal belonging to any of thegroups 7 to 11 in the periodic table or a rare earth metal. It ispreferable in particular that the metal be Ir, Pt, Ru, or Re, which isused often in light-emitting elements. These metals are noble metals.Since noble metals exist in extremely small amounts and are expensive,collecting them from light-emitting elements can significantlycontribute to reduction in cost. In particular, Ir, Pt, Ru, and Re arecommonly used as organic metal compounds which can emit visible light inreturning to a singlet ground state from a triplet excited state at roomtemperature, and can be utilized efficiently by collecting them fromlight-emitting elements.

For example, compounds represented by structural formulae shown beloware given as organic metal compounds which can emit visible light andare contained in EL layers. Note that the present invention is notlimited to these.

The organic metal compounds shown above include a metal belonging to anyof the groups 7 to 11 in the periodic table or a rare earth metal.Resources can be utilized efficiently by collecting the metal belongingto any of the groups 7 to 11 in the periodic table or the rare earthmetal from light-emitting elements containing these organic metalcompounds.

In addition to the above organic metal compounds, in particular, organicmetal compounds containing Ir as a central metal are commonly used inlight-emitting elements. For example, organic metal compounds having thefollowing partial structures are given as examples.

In addition, organic metal compounds having the above partial structuresand the following ligand are also commonly used.

As organic metal compounds having the above partial structures, forexample, compounds represented by the following structural formulae aregiven.

In addition, compounds represented by the following formulae arecommonly used in light-emitting elements.

The first electrode 202 and the second electrode 204 contain variousmetals, alloys, conductive compounds, and mixtures thereof, and thelike. For example, a transparent conductive film made of indium tinoxide (ITO), indium tin oxide containing silicon or silicon oxide,indium zinc oxide (IZO), or the like can be used for an electrodethrough which light is extracted. Further, various conductive materialssuch as gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium(Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium(Pd), or aluminum (Al) can be used. Furthermore, an element belonging tothe group 1 or 2 in the periodic table, i.e. an alkali metal such aslithium (Li) and cesium (Cs), an alkaline earth metal such as magnesium(Mg), calcium (Ca), and strontium (Sr); an alloy containing theseelements (MgAg, AlLi, or the like); a rare earth metal such as europium(Eu), and ytterbium (Yb); alloys containing these elements; or the likecan be used.

A material which emits visible light in returning to a singlet groundstate from a triplet excited state at room temperature is extracted froma light-emitting element having such a structure described above. First,the first electrode 202 or the second electrode 204 is detached from thelight-emitting element. It is acceptable as long as at least one in thepair of electrodes is detached, but it is easier to detach an electrodethat is formed after forming the EL layer. It is relatively easy todetach the electrode since an electrode made of an inorganic compoundgenerally has low adhesion to an organic compound. The electrode can bedetached by, for example, putting adhesive tape on the electrode andpeeling off the tape afterwards. In particular, the electrode which isformed on a region smaller than the EL layer, can easily be detached.

In addition to adhesive tape, it is also possible to detach theelectrode by applying a light curing resin, a heat curing resin, or thelike and peeling it afterwards. A versatile resin such as an epoxyresin, a polyimide resin, or a phenol resin can be used as the resin.

Furthermore, the electrode may be removed by acid treatment or alkalinetreatment when the electrode contains a material which is reactive withacid or alkali, such as aluminum (Al).

Thereafter, the EL layer is extracted. Various methods can be used totake out the EL layer. For example, an organic compound contained in theEL layer may be extracted in a state of solution after being dissolvedin a solvent. A solvent of aromatic hydrocarbon such as toluene, xylene,and tetralin; aromatic hydrocarbon containing halogen, such asdichlorobenzene and chlorobenzene; aliphatic halogenated hydrocarbonseries such as dichloromethane and chloroform; or the like are given asexamples of the solvent which can dissolve the organic compoundcontained in the EL layer. Further, a solvent of ether series such astetrahydrofuran and diethyl ether may also be used. Here, the EL layerneed not completely be dissolved in the solvent and may be extracted,dissolved partially in a state of a mixture.

Next, a metal atom which constitutes an organic metal compound which canemit visible light in returning to a singlet ground state from a tripletexcited state at room temperature is collected from the solution or themixture containing various compounds which constitute the EL layer.

A first method is as follows: the solution or the mixture containingvarious compounds which constitute the EL layer is subjected to heattreatment and ashed. The heat treatment may be carried out under any ofthe following: atmospheric air, an oxygen atmosphere, or a reducingatmosphere. Further, the heat treatment may be carried out with areducing agent. When the heat treatment is carried out under atmosphericair or an oxygen atmosphere, a metal oxide can be obtained. When theheat treatment is carried out under a reducing atmosphere, e.g. a H₂ gasatmosphere, a metal can be obtained. Furthermore, when the heattreatment is carried out with a reducing agent such as palladium carbon(PdC) or aluminum (Al), a metal can be obtained. When a variety ofmetals are contained in the EL layer, it is preferable that the heattreatment be carried out under a reducing atmosphere since metals can beseparated with more ease compared with metal oxides by utilizing thedifference in melting points. In addition, it is preferable that theheat treatment be carried out at a temperature of 800° C. or higher,more preferably 1000° C. or higher, in order to prevent an organicmatter from remaining.

Next, the metal or the metal oxide obtained by the above method isseparated. The metal or the metal oxide can be separated by utilizingthe difference in melting points of the metals, for example. Byutilizing the difference in melting points, the targeted metal atom canbe collected: i.e., the metal atom can be collected from the organicmetal compound which can emit visible light in returning to a singletground state from a triplet excited state at room temperature.

In addition to utilizing the difference in melting points, the targetedmetal atom can also be collected by using the following method.

First, the metal or the metal oxide obtained by the above method istreated with acid water: that is to say, it is mixed with acid water andstirred. In concrete terms, the metal or the metal oxide obtained by theabove heat treatment is reacted with water containing hydrogen chloride,hydrogen bromide, hydrogen fluoride, acetic acid, nitric acid, nitrousacid, sulfuric acid, hydrogen iodide, or the like. Heat treatment oroxidation treatment may be carried out if necessary. Oxidation treatmentmay be carried out with oxygen by introducing air, for example. Further,oxidation treatment may be carried out by mixing the metal or the metaloxide with hydrogen peroxide, whereby the metal or the metal oxide isoxidized. Furthermore, oxidation treatment may be carried out withhalogen such as iodine, chlorine, or bromine.

Thus, a metal compound of a transition metal belonging to any of thegroups 7 to 11 or that of a rare earth metal can be obtained. To bespecific, a solution of chloride, bromide, fluoride, iodide, sulfate,sulfide, nitrate, nitrite, acetate, or oxide can be obtained. Chloride,bromide, fluoride, iodide, sulfate, sulfide, nitrate, nitrite, andacetate are preferable since the solubility thereof is high.

The solution which is obtained in this manner and in which the metalcompound is dissolved may be subjected to alkali treatment. Through thealkali treatment, a hydroxide, ammonium salt, phosphonium salt, andsulfonium salt of the metal can be produced, and a solution thereof canbe obtained. Ammonium salt, phosphonium salt, and sulfonium salt arepreferable since the solubility thereof is high.

After forming the solution of the metal compound which contains atransition metal belonging to any of the groups 7 to 11 or a rare earthmetal as a central metal, the metal compound is separated from thesolution. In concrete terms, there are a method in which electrolysis iscarried out and a method in which the solution is treated with asolution containing an organic ligand.

In the electrolysis method, the transition metal belonging to any of thegroups 7 to 11 or the rare earth metal is deposited on or near anelectrode by connecting the solution of the metal compound containingthe transition metal belonging to any of the groups 7 to 11 or the rareearth metal as a central metal to a DC power source. Even if anotherkind of metal is contained in the solution, it is possible to separateonly the targeted metal with ease by carrying out the electrolysis sinceeach metal has a different ionization tendency. For the electrolysis,various solvents can be used, e.g. water, acetonitrile, or molten salt.

As a method in which the solution containing the metal compound whichcontains the transition metal belonging to any of the groups 7 to 11 orthe rare earth metal as a central metal is treated with the solutioncontaining an organic ligand, a method can be given in which thesolution containing the organic ligand is added to the solutioncontaining the metal compound, whereby the metal compound and theorganic ligand are reacted with each other to form a metal complex, andthen the metal complex is extracted using a solvent which dissolves themetal complex. In this method, it is preferable that the solvent whichdissolves the metal complex be not uniformly mixed with water.

The organic ligand mentioned here is a molecule which can form aplurality of coordinate bonds with the metal, and is also referred to asa chelate ligand. To be specific, the following substances can be givenas examples: an amine derivative, an ethylenediamine derivative, atriethylenediamine derivative, an ethylenediaminethiocarboaldehydederivative, a phenol derivative, a polyphenol derivative, a thiolderivative, a cyclic thiol derivative, an ether derivative, a cyclicether derivative, a uracil derivative, an amide derivative, ammoniumsalt, a pyridine derivative, an amino sulfide derivative, an anilinederivative, a phosphoric acid derivative, phosphonium salt, a phosphineoxide derivative, a thiourea derivative, a benzothiazole derivative, athiocarbonyl derivative, and the like. These compounds may be supportedby polymer compounds. In such a case, as the polymer compounds, thosewhich contain polystyrene, polyacrylic acid ester, polymethacrylic acidester, polyvinyl ether, polyvinyl ester, or the like as a principalchain can be used. Alternatively, the organic ligand described above maybe incorporated into a side chain of a cross-linked material of thesepolymer compounds.

For example, a compound represented by General Formula (1), a compoundrepresented by General Formula (2), and a compound represented byGeneral Formula (3) are given as an amine derivative, an ethylenediaminederivative, and a triethylenediamine derivative, respectively.

In General Formula (1), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (2), R¹ to R⁴ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (3), R¹ to R⁵ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

For example, a compound represented by General Formula (4) is given asan ethylenediaminethiocarboaldehyde derivative.

In General Formula (4), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

For example, a compound represented by General Formula (5), a compoundrepresented by General Formula (6), and a compound represented byGeneral Formula (7) are given as a phenol derivative and a polyphenolderivative.

In General Formula (5), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven as examples.

For example, a compound represented by General Formula (8) and acompound represented by General Formula (9) are given as a thiolderivative and a cyclic thiol derivative.

In General Formula (8), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven examples.

For example, a compound represented by General Formula (10), a compoundrepresented by General Formula (11), and a compound represented byGeneral Formula (12) are given as an ether derivative and a cyclic etherderivative.

For example, a compound represented by General Formula (13) and acompound represented by General Formula (14) are given as a uracilderivative.

In General Formula (13), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven as examples.

In General Formula (14), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven as examples.

For example, a compound represented by General Formula (15), a compoundrepresented by General Formula (16), and a compound represented byGeneral Formula (17) are given as an amide derivative.

In General Formula (15), R¹ and R² each independently representhydrogen, an alkyl group, or an aryl group. In concrete terms, a methylgroup, a butyl group, a hexyl group, a decyl group, a phenyl group, anaphthyl group, and the like are given as examples.

In General Formula (16), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (17), R¹ to R⁶ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

For example, a compound represented by General Formula (18) is given asammonium salt.

In General Formula (18), R¹ to R⁴ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples. Further, B⁻ represents any ofthe following: a chloride ion, a sulfate ion, a perchlorate ion, anacetate ion, a bromide ion, an iodide ion, a carbonate ion, a hydrogencarbonate ion, and a sulfite ion.

For example, a compound represented by General Formula (19) and acompound represented by Formula (20) are given as a pyridine derivative.

In General Formula (19), R¹ and R² each independently representhydrogen, an alkyl group, or an aryl group. In concrete terms, a methylgroup, a butyl group, a hexyl group, a decyl group, a phenyl group, anaphthyl group, and the like are given as examples.

In General Formula (20), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven as examples.

For example, a compound represented by General Formula (21) is given asan amino sulfide derivative.

In General Formula (21), R¹ represents hydrogen, an alkyl group, or anaryl group. In concrete terms, a methyl group, a butyl group, a hexylgroup, a decyl group, a phenyl group, a naphthyl group, and the like aregiven as examples.

For example, a compound represented by General Formula (22) is given asan aniline derivative.

In General Formula (22), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

For example, a compound represented by General Formula (23), a compoundrepresented by General Formula (24), and a compound represented byGeneral Formula (25) are given as a phosphoric acid derivative,phosphonium salt, and a phosphine oxide derivative.

In General Formula (23), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (24), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (25), R¹ to R⁴ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples. Further, B⁻ represents any ofthe following: a chloride ion, a sulfate ion, a perchlorate ion, anacetate ion, a bromide ion, an iodide ion, a carbonate ion, a hydrogencarbonate ion, and a sulfite ion.

For example, a compound represented by General Formula (26) is given asa thiourea derivative.

In General Formula (26), R¹ to R⁴ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

For example, a compound represented by General Formula (27) is given asa benzothiazole derivative.

In General Formula (27), R¹ represents hydrogen, an aryl group, or analkoxy group.

For example, a compound represented by General Formula (28), a compoundrepresented by General Formula (29), a compound represented by GeneralFormula (30), and a compound represented by General Formula (31) aregiven as a thiocarbonyl derivative.

In General Formula (28), R¹ and R² each independently representhydrogen, an alkyl group, or an aryl group. In concrete terms, a methylgroup, a butyl group, a hexyl group, a decyl group, a phenyl group, anaphthyl group, and the like are given as examples.

In General Formula (29), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

In General Formula (30), R¹ and R² each independently representhydrogen, an alkyl group, or an aryl group. In concrete terms, a methylgroup, a butyl group, a hexyl group, a decyl group, a phenyl group, anaphthyl group, and the like are given as examples.

In General Formula (31), R¹ to R³ each independently represent hydrogen,an alkyl group, or an aryl group. In concrete terms, a methyl group, abutyl group, a hexyl group, a decyl group, a phenyl group, a naphthylgroup, and the like are given as examples.

The method described above makes it possible to separate a central metalwhich constitutes a material that emits visible light in returning to asinglet ground state from a triplet excited state at room temperatureand is contained in a light-emitting element, i.e. a metal belonging toany of the groups 7 to 11 or a rare earth metal. According to the methoddescribed in this embodiment mode, resources of the metal belonging toany of the groups 7 to 11 or the rare earth metal such as iridium (Ir)and platinum (Pt), which are scarce metals, can be utilized efficiently.

Similarly, a central metal which constitutes a material that emitsvisible light in returning to a singlet ground state from a tripletexcited state at room temperature can be collected also from alight-emitting element in which a plurality of EL layers are stackedwith a charge-generating layer interposed therebetween/thereamong.

This embodiment mode can appropriately be combined with other embodimentmodes.

Embodiment Mode 2

This embodiment mode explains a method for collecting a metal atom,which is different from the method described in Embodiment Mode 1.

In a similar manner with Embodiment Mode 1, an EL layer is extracted andthen a solution or a mixture containing various compounds whichconstitute the EL layer is formed.

Next, the solution in which the EL layer is dissolved in a solvent, or amixture in which the EL layer is partially dissolved in a solvent isirradiated with microwaves. The microwaves may be adjusted so that theorganic metal compound which is contained in the EL layer and can emitvisible light in returning to a singlet ground state to a tripletexcited state at room temperature can decompose. Further, the solutionor the mixture can also be irradiated with light in microwaveirradiation. The light irradiation makes the organic metal compound inan excited state and can promote further decomposition. Furthermore, anorganic compound may be added in microwave irradiation. Acetylacetone,picolinic acid, pyridine, and the like are given as the organiccompound. Adding the organic compound can promote the decomposition ofthe organic metal compound which can emit visible light in returning toa singlet ground state from a triplet excited state at room temperature.It is preferable that a solvent used in microwave irradiation have highpolarity. Using the high-polar solvent enables the efficientdecomposition of the organic metal compound which can emit visible lightin returning to a singlet ground state from a triplet excited state atroom temperature since the value of generated heat increases inmicrowave irradiation. Glycerol, 2-ethoxyethanol, ethylene glycol,dichloromethane, or the like can be given as the high-polar solvent.Further, ionic liquid of 1-butyl-3-methylimidazoliumhexafluorophosphate,1-butyl-3-methylimidazoliumtetrafluoroborate, or the like may be used.Furthermore, water may be added to these solvents as well.

After the microwave irradiation, an operation of separating the targetedmetal from the solution or the mixture containing the decomposed matteris carried out, if necessary. As a method for separating the targetedmetal, the following methods are given: after treating the solution orthe mixture with acid water, electrolysis is carried out; after treatingthe solution or the mixture with acid, an organic ligand is added and ametal complex is extracted; or an organic ligand is added to thesolution or the mixture containing the decomposed matter and a metalcomplex is extracted directly.

The solution or the mixture containing the decomposed matter which isobtained as described above is treated with acid water. That is to say,the solution or the mixture is mixed with acid water and stirred. Inconcrete terms, the solution or the mixture containing the decomposedmatter is reacted with water containing hydrogen chloride, hydrogenbromide, hydrogen fluoride, acetic acid, nitric acid, nitrous acid,sulfuric acid, hydrogen iodide, or the like. Heat treatment or oxidationtreatment may be carried out if necessary. Oxidation treatment may becarried out with oxygen by introducing air, for example. Further,oxidation treatment may be carried out by mixing the solution or themixture with hydrogen peroxide, whereby the solution or the mixture isoxidized. Furthermore, oxidation treatment may be carried out withhalogen such as iodine, chlorine, and bromine.

Accordingly, a metal compound which contains a transition metalbelonging to any of the groups 7 to 11 or that of a rare earth metal asa central metal can be obtained. To be specific, chloride, bromide,fluoride, iodide, sulfate, sulfide, nitrate, nitrite, acetate, or oxidecan be obtained.

The solution which is obtained in this manner and in which the metalcompound is dissolved or a suspension which is obtained in this mannerand in which the metal compound is suspended may be treated with alkali.Through the alkali treatment, a hydroxide, ammonium salt, phosphoniumsalt, and sulfonium salt of the metal can be produced, and a solutionthereof or a suspension thereof can be obtained.

After forming the solution or the suspension containing the metalcompound which contains a transition metal belonging to any of thegroups 7 to 11 or a rare earth metal as a central metal, the metalcompound is separated from the solution or the suspension. In concreteterms, there are a method in which electrolysis is carried out and amethod in which the solution or the suspension is treated with asolution containing an organic ligand. Electrolysis can preferably beemployed for the solution. Treatment with a solution containing anorganic ligand can be preferably employed both for the solution and thesuspension.

In the electrolysis method, the transition metal belonging to any of thegroups 7 to 11 or the rare earth metal is deposited on or near anelectrode by connecting the solution of the metal compound containingthe transition metal belonging to any of the groups 7 to 11 or the rareearth metal as a central metal to a DC power source. Even if anotherkind of metal is contained in the solution, it is possible to separateonly the targeted metal with ease by carrying out the electrolysis sinceeach metal has a different ionization tendency. For the electrolysis,various solvents can be used, e.g. water, acetonitrile, and molten salt.

As a method in which the solution or the suspension containing the metalcompound which contains the transition metal belonging to any of thegroups 7 to 11 or the rare earth metal as a central metal is treatedwith the solution containing the organic ligand, a method can be givenin which the solution containing the organic ligand is added to thesolution or the suspension containing the metal compound, whereby themetal compound and the organic ligand are reacted with each other toform a metal complex, and then the metal complex is extracted with asolvent which dissolves the metal complex. In this method, it ispreferable that the solvent which dissolves the metal complex be notuniformly mixed with water. As the organic ligand, the organic liganddescribed in Embodiment Mode 1 can be used.

Further, by adding an organic ligand to the solution or the mixturecontaining the decomposed matter to extract a metal complex directly,the targeted metal can be separated. Also in the case of directextraction, by adding a solution containing an organic ligand to thesolution or the mixture containing the decomposed matter, the metalcontained in the decomposed matter and the organic ligand are reactedwith each other to form a metal complex, so that the metal complex canbe extracted with a solvent which dissolves the metal complex. In thiscase, as the organic ligand, the organic ligand described in EmbodimentMode 1 can be used.

The method described above makes it possible to separate a central metalwhich constitutes a material that emits visible light in returning to asinglet ground state from a triplet excited state at room temperatureand is contained in a light-emitting element, i.e. a metal belonging toany of the groups 7 to 11 or a rare earth metal.

According to the method described in this embodiment mode, resources ofthe metal belonging to any of the groups 7 to 11 or the rare earth metalsuch as iridium (Ir) and platinum (Pt), which are scarce metals, can beutilized efficiently.

This embodiment mode can appropriately be combined with other embodimentmodes.

Embodiment Mode 3

This embodiment mode explains a method for collecting a metal atom,which is different from the methods described in Embodiment Mode 1 andEmbodiment Mode 2.

In a similar manner with Embodiment Mode 1, an EL layer is extracted andthen a solution or a mixture containing various compounds whichconstitute the EL layer is formed.

Next, the solution in which the EL layer is dissolved in a solvent, orthe mixture in which the EL layer is partially dissolved in a solvent istreated with acid water. That is to say, the solution or the mixture ismixed with acid water and stirred. In concrete terms, the organiccompounds which constitute the EL layer is reacted with water containinghydrogen chloride, hydrogen bromide, hydrogen fluoride, acetic acid,nitric acid, nitrous acid, sulfuric acid, hydrogen iodide, or the like.Heat treatment or oxidation treatment may be carried out if necessary.Oxidation treatment may be carried out with oxygen by introducing air,for example. Further, oxidation treatment may be carried out by mixingthe solution or the metal mixture with hydrogen peroxide, whereby thesolution or the mixture is oxidized. Furthermore, oxidation treatmentmay be carried out with halogen such as iodine, chlorine, and bromine.Still furthermore, microwave irradiation may be carried out as the heattreatment.

Accordingly, a metal compound of a transition metal belonging to any ofthe groups 7 to 11 or that of a rare earth metal can be obtained. To bespecific, chloride, bromide, fluoride, iodide, sulfate, sulfide,nitrate, nitrite, acetate, or oxide can be obtained.

The solution which is obtained in this manner and in which the metalcompound is dissolved or a suspension which is obtained in this mannerand in which the metal compound is suspended may be treated with alkali.Through the alkali treatment, a hydroxide, ammonium salt, phosphoniumsalt, and sulfonium salt of the metal can be produced, and a solutionthereof or a suspension thereof can be obtained.

After forming the solution or a suspension containing the metal compoundwhich contains a transition metal belonging to any of the groups 7 to 11or a rare earth metal as a central metal, an operation of separating themetal compound from the solution or the suspension is carried out, ifnecessary. In concrete terms, there are a method in which electrolysisis carried out and a method in which the solution or the suspension istreated with a solution containing an organic ligand. Electrolysis canpreferably be employed for the solution. Treatment with a solutioncontaining an organic ligand can be preferably employed both for thesolution and the suspension.

In the electrolysis method, as explained in Embodiment Mode 1 andEmbodiment Mode 2, the transition metal belonging to any of the groups 7to 11 or the rare earth metal is deposited on or near an electrode byconnecting the solution of the metal compound containing the transitionmetal belonging to any of the groups 7 to 11 or the rare earth metal asa central metal to a DC power source. Even if another kind of metal iscontained in the solution, it is possible to separate only the targetedmetal with ease by carrying out the electrolysis since each metal has adifferent ionization tendency. For the electrolysis, various solutionscan be used, e.g. water, acetonitrile, and molten salt.

Further, by adding the solution containing the organic ligand to thesolution or the suspension containing the metal compound which containsthe transition metal belonging to any of the groups 7 to 11 or the rareearth metal as a central metal, the metal compound and the organicligand are reacted with each other to form metal complex, and then themetal complex can be extracted with a solvent which dissolves the metalcomplex. In this method, it is preferable that the solvent whichdissolves the metal complex be not uniformly mixed with water. As theorganic ligand, the organic ligand described in Embodiment Mode 1 can beused.

The method described above makes it possible to separate a central metalwhich constitutes a material that emits visible light in returning to asinglet ground state from a triplet excited state at room temperatureand is contained in a light-emitting element, i.e. a metal belonging toany of the groups 7 to 11 or a rare earth metal.

According to the method described in this embodiment mode, resources ofthe metal belonging to any of the groups 7 to 11 or the rare earth metalsuch as iridium (Ir) and platinum (Pt), which are scarce metals, can beutilized efficiently.

This embodiment mode can appropriately be combined with other embodimentmodes.

Embodiment 1

Hereinafter, an example where a metal is collected from an organic metalcompound which can emit visible light in returning to a singlet groundstate from a triplet excited state at room temperature according to amethod of the present invention is illustrated specifically. In concreteterms, an example where iridium is collected from an organic metalcompound containing iridium is illustrated specifically.

An iridium complex is often used for a light-emitting element because itcan emit visible light in returning to a singlet ground state from atriplet excited state at room temperature and can accomplish high lightemission efficiency. When iridium, which is a noble metal, contained inan iridium complex is collected from a light-emitting element, anelectrode of the light-emitting element may be detached using tape orthe like, and then an EL layer of the light-emitting element may bedissolved in an organic solvent. However, in the solvent in which the ELlayer is dissolved, several kinds of organic compounds can be containedin addition to the iridium complex because materials other than alight-emitting material (e.g. a hole transport material, an electrontransport material, a host material for dispersing dopant, and the like)are also usually used for a light-emitting element.

In this embodiment, on the assumption of such a situation, it isdemonstrated that a compound containing iridium can be separated from amixed solution in which three kinds of substances are dissolved: thedissolved substances are an iridium complex, a substance that can beused as a hole transport material or a host material, and a substancethat can be used as an electron transport material or a host material

<Step 1: Making a Mixed Solution>

20 mg of(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]), which is an iridium complex,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),which is a hole transport material, tris(8-quinolinolato)aluminum(III)(abbreviation: Alq₃), which is an electron transport material, are eachweighed out, and they are dissolved in 3 ml of toluene to make asolution.

<Step 2: Separating and Collecting the Compound Containing Iridium>

Next, 3 ml of 5 M hydrochloric acid solution is added to the mixedsolution which is made through the step 1, and the mixed solution towhich 3 ml of 5 M hydrochloric acid solution is added is irradiated withmicrowaves (2.45 GHz, 0 to 250 W, 0 to 250 psi) for 30 minutes to bereacted. After the reaction, black powder is deposited and the reactedsolution is separated into a light brown toluene layer and a lightyellow hydrochloric acid solution layer. It is observed that2,3-bis(4-fluorophenyl)quinoxaline, which is a ligand of an iridiumcomplex, and NPB are dissolved in the toluene layer by carrying out thinlayer chromatography to the toluene layer, which is an upper layer.Further, the hydrochloric acid solution, which is a lower layer, islight yellow and it is probable that 8-quinolinol, which is a ligand ofAlq₃, is dissolved therein. Therefore, it is probable that the compoundcontaining iridium is able to be separated by being depositedselectively. The deposited compound containing iridium is filtered,washed with toluene and then with dichloromethane, and is collected. Themicrowave irradiation is carried out using a microwave synthesisapparatus (Discover: made by CEM Corporation).

The black powder obtained in the step 2 is analyzed by electron probeX-ray microanalysis (EPMA). As a result of the analysis, it is foundthat elements detected are carbon (C), iridium (Ir), fluorine (F),nitrogen (N), chlorine (Cl), and oxygen (O) (in descending order ofdetected amounts). From this result, it is confirmed that iridium isable to be collected from the mixed solution containing[Ir(Fdpq)₂(acac)], NPB and Alq₃. Further, it is confirmed that iridiumis able to be separated from the solution containing aluminum derivingfrom Alq₃ and iridium deriving from [Ir(Fdpq)₂(acac)] as metal elementsby the above method.

This application is based on Japanese Patent Application serial no.2006-308730 filed with Japan Patent office on Nov. 15, 2006, the entirecontents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCE

-   201: substrate, 202: first electrode, 203: EL layer, and 204: second    electrode.

The invention claimed is:
 1. A method for collecting a metal from alight-emitting element which has an EL layer comprising an organic metalcompound of the metal between a pair of electrodes, the methodcomprising the steps of: exposing the EL layer by detaching one of thepair of electrodes from the light-emitting element; treating the ELlayer with a solvent to form a solution or a mixture of the organicmetal compound; heating the solution or the mixture at a temperaturehigher than 800° C. under an oxygen atmosphere to ash the organic metalcompound; and collecting the metal as a metal oxide which is obtained bythe ashing, wherein the metal is iridium or platinum.
 2. The method forcollecting the metal according to claim 1, further comprising the stepof: treating the metal oxide with acid water to form a second solutionin which the metal oxide is dissolved.
 3. The method for collecting themetal according to claim 1, further comprising the steps of: treatingthe metal oxide with acid water to form a second solution in which themetal oxide is dissolved; and electrolyzing the second solution.
 4. Themethod for collecting the metal according to claim 1, further comprisingthe steps of: treating the metal oxide with acid water to form a secondsolution in which the metal oxide is dissolved; and reacting the metalcontained in the second solution with an organic ligand to form a metalcomplex.
 5. The method for collecting the metal according to claim 1,further comprising the steps of: treating the metal oxide with acidwater to form a second solution in which the metal oxide is dissolved;reacting the metal contained in the second solution with an organicligand to form a metal complex; and extracting the metal complex using asolvent.
 6. The method for collecting the metal according to claim 1,further comprising: treating the metal oxide with acid water to fowl asecond solution in which the metal oxide is dissolved, wherein the acidwater contains a substance selected from hydrogen chloride, hydrogenbromide, hydrogen fluoride, and hydrogen iodide.
 7. A method forcollecting a metal from a light-emitting element which has an EL layercomprising an organic metal compound of the metal between a pair ofelectrodes, the method comprising the steps of: heating the EL layer ata temperature higher than 800° C. under an atmosphere containing oxygento form an oxide of the metal; and collecting the metal as the oxide ofthe metal, wherein the metal is iridium or platinum.
 8. The methodaccording to claim 7, further comprising: treating the oxide of themetal with acid water to form a solution in which the oxide of the metalis dissolved.
 9. The method according to claim 7, further comprising:treating the oxide of the metal with acid water to form a solution inwhich the oxide of the metal is dissolved; and electrolyzing thesolution.
 10. The method according to claim 9, wherein the acid watercontains a substance selected from hydrogen chloride, hydrogen bromide,hydrogen fluoride, and hydrogen iodide.
 11. The method according toclaim 7, further comprising: treating the oxide of the metal with acidwater to form a solution in which the oxide of the metal is dissolved;and reacting the oxide of the metal with an organic ligand to form ametal complex.
 12. The method according to claim 7, further comprising:treating the oxide of the metal with acid water to form a solution inwhich the oxide of the metal is dissolved; and reacting the oxide of themetal with an organic ligand to form a metal complex; and extracting themetal complex using a solvent.